Keithley 2303, User Manual

Page: 87 / 152

Status Structure 7-5
Programming and reading registers
Programming enable registers
The only registers that can be programmed by the user are the enable registers. All other reg-
isters in the status structure are read-only registers. The following explains how to ascertain the
parameter value for the various commands used to program enable registers. The actual com-
mands are covered later in this section (see Tables 7-2 and 7-5).
A command to program an event enable register is sent with a decimal parameter value that
determines the desired state (0 or 1) of each bit in the appropriate register. The bit positions of
the register (see Figure 7-2) indicate the parameter value in binary format. For example, if you
wish to sets bits B4, B3 and B1, the binary value would be 11010 (where B4=1, B3=1, B2=0,
B1=1, B0=0 and all other bits are 0). The decimal equivalent of binary 11010 is 26. Therefore,
the parameter value for the enable command is 26.
Another way to determine the decimal value is to add up the decimal weights for the bits that
you wish to set. Note that Figure 7-2 includes the decimal weight for each register bit. To set bits
B4, B3 and B1, the parameter value would be the sum of the decimal weights for those bits
(16+8+2 = 26).
Figure 7-2
16-bit status register
A) Bits 0 through 7
B) Bits 8 through 15
Reading registers
Any register in the status structure can be read by using the appropriate query (?) command.
The specific query commands are covered later in this section (see Tables 7-2 through 7-5).
The response message to the query command is a decimal value. To determine which bits in
the register are set, convert that decimal value to its binary equivalent. For example, the binary
equivalent of decimal 41 is 101001. This binary value indicates that bits B5, B3 and B0 are set.
Bit Position B7 B6 B5 B4 B3 B2 B1 B0
Binary Value 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1
Decimal Weights
128
(2
7
)
64
(2
6
)
32
(2
5
)
16
(2
4
)
8
(2
3
)
4
(2
2
)
2
(2
1
)
1
(2
0
)
Bit Position B15 B14 B13 B12 B11 B10 B9 B8
Binary Value 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1
Decimal Weights
32768
(2
15
)
16384
(2
14
)
8192
(2
13
)
4096
(2
12
)
2048
(2
11
)
1024
(2
10
)
512
(2
9
)
256
(2
8
)